Tyrosine-induced keratopathy in the rat is being done as a study of a similar human disease, the Richner-Hanhart Syndrome, in which elevated serum tyrosine causes eye and skin disease. We have previously studied biomicroscopic and light microscopic parameters of disease in the corneas of tyrosine-fed rats. We now are correlating electron microscopic appearance of disease with light and biomicroscopy. It appears that sheaves of crystal-like structures occur in the corneal epithelial defects in 36 to 60 hours. These sheaves or bundles transfix and penetrate cells and nuclei, and are visible in polarized light. If they are identified as tyrosine crystals, a new disease mechanism with some relationship to intracellular and extracellular pathology in cystinosis and gout will have been identified. The serum and aqueous humor levels of tyrosine are being studied during the course of tyrosine-induced keratopathy, and related to the other parameters of disease, as well as regulation by an inducible enzyme, tyrosine aminotransferase. The effect of adrenalectomy as well as administration of adrenal corticosteroids on tyrosine-induced keratopathy and serum tyrosine levels is under study.